Various types of fasteners are used to fasten implants and other devices to bones. In a spinal field, bone screws are typically used in order to attach plates, rods, and the like of implants and devices to one or more vertebral bodies.
Various techniques have been developed to fix the bone screws to the vertebral bodies, or prevent the bone screws from being separated from the plates or rods of the implants and devices. For example, U.S. Pat. No. 7,846,207 discloses a technique in which a cage may be inserted between vertebral bodies and bone screws may be attached to the vertebral bodies to fix the cage. The above patent proposes a method in which, a securing plate is further provided on a head side of the bone screw to prevent the bone screw from being pulled out, and the securing screw is coupled to the cage by passing it through the securing plate.
In addition, U.S. Pat. No. 6,398,783 discloses a locking element that rotates around a hole into which the bone screw is inserted, which is installed in a plate to prevent the bone screw from being pulled out when fixing the plate to the vertebral body.
Further, U.S. Pat. No. 7,625,379 discloses using two nuts in an SI joint fusion implant to prevent the bone screw from being pulled out, which is used when a problem occurs in a joint between a sacrum and an ilium (pelvis).
As such, various techniques for preventing the bone screw from being pulled out in various areas are considered and disclosed in the art, but there is a disadvantage that a separate locking mechanism should be used for this purpose. Therefore, there is a need to develop a screw which can easily maintain the locked state without the separate locking mechanism.